Energy Recovery System for a Mobile Machine

ABSTRACT

The disclosure is directed to an energy recovery system for a mobile machine The energy recovery system may include a tank configured to store a liquid fuel for combustion within an engine of the mobile machine, and a first reservoir configured to receive gaseous fuel formed in the tank. The energy recovery system may also include a conduit disposed around the tank that may be fluidly connected to the first reservoir. The energy recovery system may also include a second reservoir fluidly connected to the conduit, and an energy recovery configured to generate work utilizing a temperature gradient between gaseous fuel disposed within the first and second reservoirs.

TECHNICAL FIELD

The present disclosure relates generally to a recovery system, and more particularly, to an energy recovery system for a mobile machine.

BACKGROUND

Natural gas has been used an alternative fuel for internal combustion engines in mobile machines. Because natural gas has a lower energy density than traditional fuels such as diesel and gasoline, mobile machines generally utilize liquefied natural gas (“LNG”). At atmospheric pressures, natural gas must be chilled to below about −160° C. to remain in liquid form. Mobile machines utilizing LNG as a fuel store the LNG in insulated tanks. Because these tanks are not perfect insulators, heat enters the tank, causing some of the LNG to boil (“boil-off”). The boil-off increases the pressure of the tank, and can cause the tank to explode if not removed. Traditional. LNG systems vent the boil-off (composed mostly of methane) directly to the atmosphere. However, because methane is a greenhouse gas, government regulations no longer permit the direct venting of boil-off to the atmosphere.

One method of handling boil-off from an LNG tank is described in U.S. Patent Publication No. 2008/0053349 (“the '349 publication”) of O'Connor that published on Mar. 6, 2008. The '349 publication describes a marine vessel having a tank for storing LNG. The '349 publication delivers boil-off gas from the tank to a combustion section via a gas inlet. Combustion air is also directed to the combustion section and the resulting air-gas mixture is ignited. This system effectively converts the boil-off to carbon dioxide and water, which are less harmful to the environment.

Although the system of the '349 publication may be capable of preventing boil-off from directly venting to the atmosphere, it may be wasteful. Specifically, because the system of the '349 publication only combusts the boil-off, energy associated with the boil-off is lost from the system as heat and exhaust.

The energy recovery system of the present disclosure solve one or more of the problems set forth above and/or other problems with existing technologies.

SUMMARY

In one aspect, the disclosure is directed to an energy recovery system for a mobile machine. The energy recovery system may include a tank configured to store a liquid fuel for combustion within an engine of the mobile machine, and a first reservoir configured to receive gaseous fuel formed in the tank. The energy recovery system may also include a conduit disposed around the tank that may be fluidly connected to the first reservoir. The energy recovery system may also include a second reservoir fluidly connected to the conduit, and an energy recovery device configured to generate work utilizing a temperature gradient between gaseous fuel disposed within the first and second reservoirs.

In another aspect, the disclosure is directed to a method of operating a mobile machine. The method may include directing gaseous fuel formed in a tank through a conduit disposed around the tank, and generating work utilizing a temperature gradient between gaseous fuel disposed within a first reservoir and a second reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial illustration of an exemplary disclosed mobile machine; and

FIG. 2 is a diagrammatic illustration of an exemplary disclosed energy recovery system that may be used in conjunction with the mobile machine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of a mobile machine 10, such as a locomotive, that includes a car body 12 supported at opposing ends by a plurality of trucks 14 (e.g., two trucks 14). Each truck 14 may be configured to engage a track 16 via a plurality of wheels 17, and support a frame 18 of car body 12. Any number of engines may be mounted to frame 1$ and configured to produce electricity that drives wheels 17 included within each truck 14, in the exemplary embodiment shown in FIG. 1, mobile machine 10 includes a main engine 20.

Mobile machine 10 may also include a tank 24 configured to store a liquid fuel for combustion within main engine 20. Tank 24 may be an insulated, single or multi-walled tank configured to store a liquid fuel at low temperatures, such as below about −160° C. Tank 24 may be mounted to a frame 26 configured to be pulled by mobile machine 10. Frame 26 may be supported by a plurality of trucks 28 (e.g., two trucks 28). Similar to truck 14, each truck 28 may be configured to engage track 16 via a plurality of wheels 30. Alternatively, tank 24 may be mounted to frame 18, if desired. An insulating conduit 32 may be disposed around tank 24. In one exemplary embodiment, insulating conduit 32 may include a plurality of coils wrapped around tank 24 to substantially enclose and insulate tank 24 from ambient air and sunlight radiation.

As shown in FIG. 2, mobile machine 10 may be equipped with an energy recovery system (“system”) 200 that is configured to generate work by utilizing boil-off gas formed in tank 24. System 200 may include, among other things, a fuel delivery circuit 202 and a boil-off circuit 204. Fuel flows may be regulated through fuel delivery circuit 202 by a controller (not shown).

Fuel delivery circuit 202 may include components that cooperate to deliver a liquid fuel stored in tank 24 to main engine 20. Fuel delivery circuit 202 may include, among other things, conventional pumps, conduits, heat exchangers, accumulators, and injectors configured to condition and deliver low-temperature liquid fuel from tank 24 to main engine 20 in gaseous form, as is known in the art. During this conditioning and delivery, some fuel within tank 24 may evaporate into a gaseous fuel.

Boil-off circuit 204 may include components that cooperate to generate work utilizing the boiled-off gaseous fuel formed within tank 24. In particular, boil-off circuit 204 may include a control valve 212, a first reservoir 214, a second reservoir 216, an energy recovery device 218, and a combustion chamber 220. Gaseous fuel may flow from tank 24 through control valve 212 to first reservoir 214. From first reservoir 214, gaseous fuel may be directed toward an inlet of insulating conduit 32 that may be fluidly connected to first reservoir 214. Gaseous fuel flowing through insulating conduit 32 may be heated by ambient air or by sunlight radiation and flow toward second reservoir 216 that is fluidly connected to an outlet of insulating conduit 32.

Control valve 212 may be a controllable pressure-relief valve configured to selectively allow fluid communication between tank 24 and first reservoir 214. When control valve 212 opens, it may allow gaseous fuel to escape tank 24 and flow to first reservoir 214. Control valve 212 may include a spring-loaded mechanism (not shown) that opens control valve 212 at a predetermined pressure to avoid over-pressurization of tank 24. Additionally or alternatively, control valve 212 may include one or more controllable actuators, such as one or more electric solenoids that are operable to open control valve 212 when activated.

First and second reservoirs 214 and 216 may embody, for example, suitable vessels configured to store gaseous fuel. First and second reservoirs 214 and 216 may be arranged on opposite ends of, and be in thermal communication with, energy recovery device 218.

Energy recovery device 218 may be a device capable of utilizing a temperature gradient between first and second reservoirs 214 and 216 to generate work. In one exemplary embodiment, energy recovery device 218 may be a Stirling engine. Any suitable Stirling engine may be utilized, including a displacer-type Stirling engine, a two-piston Stirling engine, or another suitable Stirling engine. The Stirling engine may include a working fluid disposed within a closed chamber (not shown). The working fluid may go through steps that cause a mechanical linkage (not shown) to perform work. For example, during a pressure-increase step, heat from second reservoir 216 may increase a pressure of the working fluid, causing the mechanical linkage to move. Heat generated by the pressure-increase step may be removed from the Stirling engine via first reservoir 214 so that the cycle can be repeated. That is, first reservoir 214 may function as a heat sink for heat utilized and generated by the Stirling engine. The mechanical output of the Stirling engine may be used to perform mechanical work, such as driving a pump (not shown), or may be used to generate electricity via a. generator (not shown).

In another exemplary embodiment, energy recovery device 218 may be a thermoelectric device configured to generate electricity utilizing a temperature gradient between first and second reservoirs 214 and 216. The thermoelectric device may utilize suitable combinations of metals, ceramics, semiconductors, or other suitable materials to harvest and/or convert thermal energy from the gaseous fuel within second reservoir 216 to generate useful electric power.

Gaseous fuel may flow from second reservoir 216 toward combustion chamber 220 via a line 222. Combustion chamber 220 may be a burner, an auxiliary engine, or another suitable combustion chamber configured to combust gaseous fuel utilized by boil-off circuit 204. In another exemplary embodiment, gaseous fuel may flow from second reservoir 216 toward main engine 20 via a line 224.

INDUSTRIAL APPLICABILITY

The disclosed energy recovery system 200 may be applicable to any mobile machine utilizing a low-temperature liquid fuel. The disclosed energy recovery system 200 may enhance fuel efficiency by using boil-off gaseous fuel to simultaneously insulate a fuel storage tank and perform useful work. The flow of gaseous fuel through recovery system 200 will now be described.

Fuel may be stored in tank 24 under pressure and low temperatures to maintain the fuel in a liquid state. In one exemplary embodiment, liquid fuel is stored in tank 24 and must be maintained at a temperature below the boiling point of the liquid fuel. Because tank 24 may not be a perfect insulator, a variety of external factors may contribute to boil-off gas formation within tank 24. For example, heat may be introduced into tank 24 via thermal conduction with ambient air or by sunlight radiation. Such heat may cause some liquid fuel within tank 24 to boil and convert to gaseous form.

When a sufficient amount of boil-off gas accumulates within tank 24, a pressure of tank 24 may reach a threshold such that control valve 212 opens, releasing boiled-off gaseous fuel to first reservoir 214. It should be noted that the temperature of the gaseous fuel within first reservoir 214 may be approximately equal to the boiling point of the gaseous fuel, From first reservoir 214, gaseous fuel may flow through insulating conduit 32. Heat may be transferred to gaseous fuel carried by insulating conduit 32 via thermal conduction with ambient air, via sunlight radiation, or other mechanisms, The gaseous fuel flowing through insulating conduit 32 may act as an insulator for tank 24, as heat may be transferred to the flowing gaseous fuel, instead of directly to tank 24.

From insulating conduit 32, gaseous fuel may flow toward second reservoir 216. While flowing through insulating conduit 32, the temperature of the gaseous fuel may increase to the ambient temperature or higher. In one exemplary embodiment, when the gaseous fuel is liquid natural gas, the temperature gradient between first and second reservoirs 214 and 216 may be about 200° C. However, it should be noted that the temperature gradient may vary depending on the gaseous fuel selected, ambient air temperature, and sunlight intensity. The temperature gradient between the gaseous fuel within first reservoir 214 and the gaseous fuel within second reservoir 216 may cause energy recovery device 218 to generate work.

In one exemplary embodiment, when energy recovery device 218 is a Stirling engine, the temperature gradient between first reservoir 214 and second reservoir 216 generates mechanical work. This mechanical work may be used to drive a mechanical load such as a pump, or may be used to drive a generator to produce electrical power. In another exemplary embodiment, when energy recovery device 218 is a thermoelectric device, the temperature gradient may cause the thermoelectric device to exploit a temperature gradient between gaseous fuel within first and second reservoirs 214 and 216 to produce electric power.

The disclosed energy recovery system 200 may provide a mechanism for improving fuel efficiency of mobile machine 10. For example, the disclosed energy recovery system 200 may use boil-off gas from tank 24 to generate work and insulate tank 24. Energy recovery system 200 may thus utilize energy from boil-off gas that otherwise would be lost, reduce liquid fuel consumption by reducing the amount of energy directed toward auxiliary loads, and reduce boil-off formation by insulating tank 24.

it will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed energy recovery system without departing from the scope of the disclosure. Other embodiments of the energy recovery system will be apparent to those skilled in the art from consideration of the specification and practice of the energy recovery system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 

What is claimed is:
 1. An energy recovery system for a mobile machine, comprising: a tank configured to store a liquid fuel for combustion within an engine of the mobile machine; a first reservoir configured to receive gaseous fuel formed in the tank; a conduit disposed around the tank and fluidly connected to the first reservoir; a second reservoir fluidly connected to the conduit; and an energy recovery device configured to generate work utilizing a temperature gradient between gaseous fuel disposed within the first and second reservoirs.
 2. The energy recovery system of claim 1, wherein the energy recovery device is in thermal communication with the first and second reservoirs.
 3. The energy recovery system of claim 1, wherein the energy recovery device is a Stirling engine.
 4. The energy recovery system of claim 1, wherein the energy recovery device is a thermoelectric device.
 5. The energy recovery system of claim 1, further including a control valve associated with the tank and configured to discharge gaseous fuel from the tank to the first reservoir when a pressure of the tank exceeds a tank threshold pressure.
 6. The energy recovery system of claim 1, further including a fuel delivery circuit fluidly connected to the tank and configured to deliver liquid fuel from the tank to the engine.
 7. The energy recovery system of claim 1, wherein the conduit substantially encloses and is coiled around the tank.
 8. The energy recovery system of claim 1, further including a combustion chamber configured to receive gaseous fuel from the second reservoir.
 9. The energy recovery system of claim 1, wherein the engine is configured to receive gaseous fuel from the second reservoir.
 10. A method of operating a mobile machine, comprising: directing gaseous fuel formed in a tank through a conduit disposed around the tank; and generating work utilizing a temperature gradient between gaseous fuel disposed within a first reservoir and a second reservoir.
 11. The method of claim 10, wherein the conduit is disposed between the first and second reservoirs.
 12. The method of claim 10, further including directing gaseous fuel from the second reservoir toward a combustion chamber or an engine of the mobile machine.
 13. The method of claim 10, further including driving a Stirling engine to generate work utilizing the temperature gradient.
 14. The method of claim 10, further including driving a thermoelectric device to generate Work utilizing the temperature gradient.
 15. The method of claim 10, further directing the gaseous fuel formed in the tank through a plurality of coils disposed around the tank.
 16. The method of claim 10, further including directing liquid fuel from the tank through a fuel delivery circuit for combustion within a main engine of the mobile machine.
 17. A mobile machine, comprising: a frame; a main engine mounted to the frame; a tank configured to store a liquid fuel; a fuel delivery circuit fluidly connected to the tank and configured to deliver fuel from the tank to the main engine; a first reservoir configured to receive gaseous fuel formed in the tank; a conduit disposed around the tank and fluidly connected to the first reservoir; a second reservoir fluidly connected to the conduit; and an energy recovery device configured to generate work utilizing a temperature gradient between gaseous fuel disposed within the first and second reservoirs.
 18. The mobile machine of claim 17, wherein the energy recovery device is a Stirling engine.
 19. The mobile machine of claim 17, wherein the energy recovery device is a thermoelectric device
 20. The mobile machine of claim 17, further including a control valve associated with the tank and configured to discharge gaseous fuel from the tank to the first reservoir when a pressure of the tank exceeds a tank threshold pressure. 